U.S. Pat. Nos. 4,942,700, 5,024,031, 6,082,056 and 6,219,974, hereby incorporated by reference as if fully disclosed herein, teach methods for constructing reversibly expandable truss-structures in a wide variety of shapes. The teachings therein have been used to build structures for diverse applications including architectural uses, public exhibits and unique folding toys.
Utilizing the teachings of these patents, self-supporting structures that maintain their overall shape as they expand or collapse in a synchronized manner may be constructed. A basic building block of such structures is a “loop-assembly” which consists of three or more scissor units (disclosed in the '700 and '031 patents) or polygon-link pairs (disclosed in the '056 and '974 patents), each consisting of a pair of links that are pinned together at pivots lying near the middle of each link. Such a loop assembly comprises a ring of interconnected links which can freely fold and unfold. However, at the center of such a ring, a space or void is opened up as the ring expands, resulting in lessened structural stability.
It is, therefore, desirable to provide additional stability and structural stability to such a loop assembly while retaining its ability to expand and contract. It is also desirable to provide a central location to provide a means to mechanically drive the entire assembly.
In accordance with the present invention a novel loop assembly is presented that incorporates an additional useful feature. I have discovered a way to provide a link-pair that lies at the center of the assembly. The middle pivot of this central link-pair is located at the center point of the assembly as a whole. Further, this pivot always maintains its location at the center of the loop assembly as it extends and retracts.
Loop assemblies having such central link-pairs are better stabilized and better self-supported than those without such a feature. The movement of structures built from such assemblies are better synchronized. Further, central link-pairs offer a conveniently placed point of control for folding structures. By simply introducing a rotary motion of one such link relative to its paired link, a force is translated in an even, symmetric fashion to the entire assembly, thereby opening and closing it. Thus, a motor may be conveniently attached to one central link and the motor shaft fixed to the paired central link to provide a well-placed, stabilized means to drive the entire assembly.
Further, in addition to such mechanical improvements, such central link-pairs lead to new functional applications, such as the construction of expanding wheels and spreading mechanisms.